Pergamon 1. Aerosol Sci. Vol. 29, Suppl. 1. pp. S9094910, 1998

8 1998 Published by Elsevier Science Ltd. All rights rwrvcd Prinrad in Gnat Britain

0021-8502t98 $19.00 + 0.00

PREPAitATION OF Y,O,:Eu PHOSPHOR WITHOUT POST-TREATMENT BY GAS PHASE REACTION

S B. PARK, Y. C. KANG, I. W. LENGGORO’, and K. OKUYAMA’

Department of Chemical Engineering, Korea Advanced Institute of Science and Technology, 373-1, Kusong-dong, Yusong-gu, Taejon, Korea, 305-701

‘Department of Chemical Engineering, Hiroshima University, l-4- 1, Kagamiyama, Higashi-Hiroshima 739-8527, Japan

KEYWORDS yttrium oxide, phosphor, ultrasonic spray pyrolysis, gas phase reaction

Good phosphor materials should have narrow size distribution, non-agglomeration, and spherical morphology for high luminescent characteristics. The mean size of particles is directly related to resolution of display and efftciency of luminescence (Sievers et al., 1997; Jiang et al., 1997). It is known that the optimum size of phosphor particles is around I urn. Spherical morphology is also required for high brightness and high resolution. In our previous works, spray pyrolysis was applied to the preparation of rare-earth doped oxide phosphor materials(Kang et al., 1997a, b). However, annealing process was necessary for crystallization and activation of as-prepared particles in the spray pyrolysis. In this work, Y,O,:Eu phosphor particles were directly prepared from mixed nitrate solutions by ultrasonic spray pyrolysis.

The particles prepared at 500 “C have broad peaks of Y,O,, and sharp peaks were obtained above 600 “C. The crystallinity of particles was increased with increasing the reactor temperatures. The particles are well crystallized at low temperatures and very short residence time owing to the fine size of particles in the gas phase. The particles had spherical morphology and non-aggregation.

In our previous works, the particles prepared by spray pyrolysis did not show any fluorescence characteristics without annealing because of short residence time. On the other hand, bright red light was obtained from the as-prepared particles of Y,O,:Eu, which has simple composition in comparison with other multicomponent phosphors. The as-prepared particles absorbed excitation energy in the range from 220 nm to 280 nm, and the maximum excitation wavelength was near 243 nm. In Fig.1, luminous intensities of the as-prepared particles at different doping concentrations of Eu were shown. The particles were prepared at the conditions of 900 “C and 2Nmin for the investigation of optimum doping concentrations. The optimum brightness was obtained at the doping concentration of 6 at.%. The main emission peak was 612 nm, resulting in a red emission.

The emission characteristics of rare-earth doped phosphor particles are strongly affected by crystallinity and dispersion efficiency of activator. In Fig.2, the effect of preparation temperature on the brightness of Y,O,:Eu particles was shown. The red light was observed from 600 “C when the prepared particles were excited with UV light. This result was consistent with the the XRD spectra, which indicated that the well crystallized Y,O, was obtained above 600 “C. The brightness of the as-prepared particles was increased with increasing temperatures because of good activation and high crystallinity in high temperatures. In the spray pyrolysis, crystallization and

s910 Abstracts of the 5th International Aerosol Conference 1998

activation of dopant were directly occurred at short residence times because of good mixing of each component inside submicron size particles. In Fig.2, the PL intensity of annealed particles was increased by 1.3 times in comparison with the as-prepared particles at 120O”C(A1200 “C). The brightness of phosphor is strongly affected by crystallinity of particles. Therefore, temperature higher than 1200 “C is required for high brightness of Y,O,:Eu phosphor in this spray pyrolysis system.

REFERENCES

Sievers, R. E., P. D. Milewski, C. Y. Xu, and B. A. Watkins, (1997) Proceeding of Third Ittterttatiottal Cottjerence on the Science and Technology of Display Phosphors, 3 03 -3 06

Jiang, Y. D., 2. L. Wang, F. Zhang, H. P. Paris, and C. J. Summers, (1997) Proceeding of Third Ittterttafiottal (bttjierence ott the Science attd Techttology of Display lYlo.~[dlol:v, 26 I -264

Kang, Y. C., J S. Choi, S. B. Park, S. H. Cho, J. S. Yoo, and J. D. Lee, (1997) .I. Atwsol Sci.. 28[S I] 54 I-542

Kang, Y. C., J. S. Choi, S. B. Park, S. H. Cho, J. S. Yoo, and J. D. Lee, (1997) Proceedittg of Third International Conference on the Science and Itchttology of

Display Phosphors, 2 5 7-260 400, 1

.z E 300

E - E 200 8 2

.s E 100

3

0

Fig. 1 Relative

550 660 650 760

Wavelength (nm) PL intensities of Y,O,:Eu particles of different doping concentrations

i? 600-

E E - E 400. p:

500 Xi0 650 760

Wavelength (n.m Fig.2 Emission spectra of Y,O,:Eu partrcles at dt d erent preparation temperatures.